As one type of coil element, a wire-wound coil element is known. For example, Japanese Patent Application Publication No. 2004-6904 (the '904 Publication) describes an electronic element formed of an insulating substrate on which a Cu wire is wound, a terminal of which is embedded by thermocompression bonding in an electrode (a Sn—Cu plated layer) formed on said insulating substrate and brazed in that state.
Furthermore, Japanese Patent Application Publication No. 2010-171054 (the '054 Publication) discloses a wire-wound electronic element having a core on which a conductor wire is wound, an upper flange and a lower flange formed at an upper end and a lower end of the core, respectively, and a pair of external electrode portions formed at different positions in a bottom end portion of the lower flange and configured to receive both terminal portions of the conductor wire connected thereto, respectively. The above-described external electrode portions each have a concave portion including a groove formed on a bottom surface of the lower flange and solder filled in the concave portion, and are configured so that the terminal portions of the conductor wire led into the groove are embedded in the solder.
In recent years, with improvement in performance of electronic devices including portable devices, there is a demand for higher performance of elements used in such electronic devices. Particularly, for portable devices, emphasis is often placed on power consumption, leading to a demand for a reduction in resistance of coil elements.
A configuration of the '904 Publication, however, presents a problem that a wire used therein has a relatively thin diameter of 20 μm to 60 μm, and thus a reduction in resistance of a coil element based on a wire cross-sectional area can hardly be achieved. On the other hand, according to a configuration of the '054 Publication, a conductor wire having a thickness of 30 μm to 350 μm can be used, and thus this configuration is advantageous in achieving a reduction in resistance. This method, however, requires that a large amount of solder be filled in the concave portion so that connection is securely established and consequently presents a problem that a size reduction can hardly be achieved due to a thickness of the solder.
On the other hand, in the method in which an end portion of a conductor wire is joined to an electrode by thermocompression bonding, the conductor wire has a width larger than its height (thickness) in a joint layer, so that it becomes likely that stress in a width direction is applied to the conductor wire. This has let to a problem that a defect such as a crack occurs in the joint layer, and thus when the joint layer is subjected to a load such as thermal stress or a drop impact, joint strength is decreased significantly.